The invention relates to a junction piece for releasably connecting rod-shaped structural elements. The system consists of a junction ball and pin elements which may be radially screwed into the ball, and which are capable of being inserted, via a cylindrical section, into front end recesses provided in the rod-shaped structural elements and axially fixed therein.
Junction pieces of this class (see e.g., DE-OS No. 2420864) serve for forming frames for the assembly of racks, shelves, and tables by means of rod-shaped structural elements and balls. The junction piece assembly formed by the rod-shaped structural elements and balls is required to be tension-proof in the best possible way, but be made releasable for disassembly to be carried out at a later date should new elements have to be added or if such framework structures and shelves have to be assembled and disassembled. Such framework structures should not only allow filling elements to be inserted, but should be made such that, for example, the square opening formed by rod-shaped structural elements and balls would be entirely filled up by means of a convenient rectangular plate. This feature is absolutely necessary for forming framework walls, shelf plates and furniture wall elements. Furthermore, the appearance of the junction piece must visually merge for most of the specified applications, i.e., apart from the rod-shaped structural element and the ball itself no other junction elements should still be visible upon completion of the assembly of the junction piece. The ball should be so arranged on the front end of its respective rod-shaped structural element that the combination of the ball and structural element looks like a mono-piece element.
The junction piece of the present invention is of the kind which consists of pin elements having an annular, groove-shaped recess with side walls of truncated conical form. The front end of a fastening screw is screwed into the cylindrical wall of the rod-shaped structural elements and is arranged to be moved against the side wall away from the junction piece. At least at their front ends, the pin elements have screwable pin element projections capable of being screwed into the threaded bores of the junction ball. The combination of the annular groove-like recess, the side walls of truncated conical form, and the fastening screw (which is adapted to be moved against the side wall away from the junction ball and to be screwed into the cylindrical wall) allows the cylindrical wall and the ball to be firmly tightened in an axial direction against one another. Thus, access to the fastening screw from outside as well as easy accessibility even in case of a most sophisticated configuration of the assembled rod-shaped structural element junctions is ensured. The length of the rod-shaped structural elements which are used will not be limited by this type of junction. Furthermore, the axial spacing of the ball from the annular front end of the cylindrical rod will be determined in a true-to-dimension manner through the ball's contact with the annular rim.
As long as the longitudinal axes of the rod-shaped structural elements connected together by means of this known junction piece are rectangular with respect to each other, assembly and disassembly of the frames do not raise any difficulties. However, if frame systems are required to be made, for example, with diagonal junctions, (i.e. junctions in which the longitudinal axes of the rod-shaped structural elements proceed at acute or obtuse angles with respect to each other,) then it will be practically impossible to subsequently insert a rod-shaped structural element into a cubical frame shelf, for example. This is because the positions of the junction balls which are to receive between them the rod-shaped structural elements are confined by the already existing frame construction. The spacing of the balls cannot be increased any more to accommodate the length of the threaded projections of the pin elements for the insertion of a diagonal rod, so that the threaded projections may subsequently be screwed into the threaded bores of the junction balls.
It is the primary object of the invention to create a junction piece accommodating rod-shaped structural elements whose axial length corresponds to the spacing between both junction balls intended to receive between them the rod-shaped structural element concerned, but which allows the threaded pin projections of the structural elements to be screwed into the threaded bores of the junction balls.